Tower Bridge is the most iconic of the structures that cross the River Thames in London. Discussion of a crossing near to the Tower of London began in 1876. The design was brought forward by the City of London architect, Sir Horace Jones (1819-87) and put into effect by the engineer Sir John Wolfe Barry (1836-1918).
The 61 m central span is a bascule bridge, while the side spans between the 65 m high towers and the river banks are suspension bridges. The lifting spans were originally raised by hydraulic power, with accumulators and two 360 hp steam engines supplied by Sir W G Armstrong, Mitchell & Co of Newcastle-upon-Tyne. The steel frames of the towers were clad in Cornish Granite and Portland Stone, and are ornamented in the Gothic style. Construction occupied eight years and the bridge was opened in 1894. The structure is owned and operated by Bridge House Estates, a charitable trust responsible to the City of London Corporation. An electro-hydraulic drive system replaced the steam engines and the original hydraulic accumulators in 1974, but the latter have been retained and now form part of a display that has been open to the public since 1982.
Visitors are able to see the engine rooms on the south bank, and to cross the river on the high level walkway which was a public right of way until 1910 when it was closed because its reputation as a haunt of prostitutes and pickpockets made people reluctant to use it.
The bridge remains a vital part of the road system in London, and is opened for ships to pass about a thousand times a year.